The moon As seen through a telescope

General features The Moon (and other bodies) were originally thought to have an atmosphere And living beings (selenites on the Moon) Therefore, it was assumed that water and land existed Easy to see on the Moon Names of features go back to 17 th C

Lunar oceans Mare (singular), maria (plural) –Dark –Smooth –Low –Often circular –Often large (Imbrium ~1100 km) –Therefore, they had to be water

Highlands Lighter in color (reflectivity/albedo) Rough High (as much as 25,000 ft) Irregular in shape Thought to be the continental areas

Minor features Craters –Microscopic to few hundreds of km –Many clearly visible by naked eye –Seen by Galileo –Named after scientists, philosophers of antiquity (and others) Valleys –In the highlands –Not common

Minor features Rilles –Sinuous Like empty river beds –Straight Long linear valleys Rays –Bright streaks radial to craters –Small to large

Minor features Regolith –Lunar soil –Gravelly –Difficult to see real bed rock

Gross features – EarthMoon –Density –Gravity 11/6 –Escape V –(Km/sec)

First (Serious) Study of Moon 1962 Shoemaker and Hackmann Shoemaker – geologist Hackmann – geographer Assumption –Maria formed by enormous impacts –Law of superposition holds for the Moon –Mare material is basalt lava

Law of superposition Simple case – sedimentary rocks

Application to impact

S and H chose Mare Imbrium –Northeast part of the near side –Large circular mare –Surrounded by mountains

Maria on the near-side of the Moon

Immediate vicinity of Mare Imbrium

Procedure Isolate the area including M Imbrium And the surrounding region –Specifically –Copernicus –Eratosthenes Determine the sequence of events

Time Absolute –Specify the age in time units –Example: the Onondaga limestone was formed 380 million years ago Relative –Specify the age in non-time units –Example: the Edwardian age in England –The Elizabethan age

Argument M. Imbrium was formed by impact Created ejecta blanket If Copernicus was older, it would have been buried But Copernicus is visible Therefore, Copernicus is younger than the impact that formed M. Imbrium

Further, M. Imbrium is filled with lava Therefore, the lava came after the impact that formed M. Imbrium Copernicus is situated on some of the mare material Therefore, Copernicus is younger that the lava

Chronology of the Moon Sequence of events The time units are named (relative time) Names are taken from the feature in question Thus, the crater Copernicus was created in Copernican time (note the different spelling)